fix bug when a practice chapter has no initial comment
fix bug when a practice chapter has no initial comment

the comment from the former chapter would stay displayed

luanlv/lila,luanlv/lila,arex1337/lila,arex1337/lila,arex1337/lila,arex1337/lila,luanlv/lila,arex1337/lila,luanlv/lila,luanlv/lila,luanlv/lila,arex1337/lila,arex1337/lila,luanlv/lila